Testing apparatus



March 8,1938. A, v, DE -r' 2,110;759

TESTING APPARATUS Filed July 19, less Y Y mm INVENTOR 22 I I Wildfire l- Patented Mar. 8,- 1 938 Alfred V. dc Forest, Southport, Conn.,

toMag naiiux Corporation.

assignor Pittsburgh, Pa... a

corporation of Pennsylvania Application July 19, 1935. Serial No. 32,165"

9 Claims.

The present invention relates to testing apparatus, and moreespecially to apparatus for the magnetic testing-of objects of paramagnetic material.

In my prior patent, No.;1,960,898, I have explained the testing of objects of paramagnetic material, such, for example, as iron and steel articles, to detect cracks, flaws, etc. in the metal. Briefly stated, the method comprises magnetizing the article and applying to the surface of the article finely divided magnetic materiaL There is a tendency for the finely divided particles to cluster on the surface at places wherev there is a crack or flaw. In this way cracks or flaws may be detected, although'not visible to the eye.

The present invention relates to improved apparatus for carrying out testing of this character. In this apparatus the test piece maybe subjected to magnetization by means of an electromagnet, and also magnetization by means of an electric current passed through the test piece. As hereinafter explained, the piece can thus be subjectedto magnetic lines of force in different elevating mechanism; and

directions so as to better detect both longitudinal and transverse cracks. The apparatus is also provided with means for demagnetizing the article.

In the drawing- 7 Figure 1 is a diagrammatic view showing one form of apparatus embodying the invention:

Figure 2 is adetail view showing the preferred form of switch for breaking the alternating current when used for magnetizing;

Figure 3 is a detail view Figure 4 is a diagrammatic view of a modified form of apparatus.

Referring to the embodiment illustrated in Figure l, the test piece 2 is supported on pole pieces 3 and 4 of the electromagnet 6; For simplicity the test piece is shown as a shaft, although other objects may be tested. preferably objects of greater length than width with thetype of apparatus illustrated in Figure 1. The pole pieces 3 and l are adjustable along the core bar 6 of the electromagnet 5 in order to accommodate objects of diflerent length. The core and pole pieces of the electromagnet are preferably made of laminated soft steel sheets to cut down eddy currents when alternating current is employed. Carried by th pole pieces 3 and l are electric contact pieces 1 and 8 insulated from the pole pieces by means'pf insulation 9. These electric contact pieces may be raised or lowered by means of the elevating mechanism shown in Figure 3 of the current contact which consists of two toothed wheels i0 insulated from the pole pieces having cam surfaces Ii and operated by means of a handle l2. When the object is to betested .by means of the electromagnet 5, the electric contacts 1 and 8 are lowered to allow the objects to come in direct contact with the pole ,pieces 3 and 4. When the object is to be tested by passing the electric current through it,the electric contact pieces i and 8 are raised to lift the test piece off of the pole pieces 3 and I.

The test piece may be tested by means of applied magnetism from the electromagnet 5. When this is done the lines of electromagnetic flux tend to run longitudinally of the test bar 2, creating a testing condition most favorable for detecting laterally extending cracks which are at right angles to the major axis of the test piece 2.

The test piece can also be subjected to magnetization so that the magnetic lines of flux lie circumferentially of the test piece 2 and at right angles to the length of the test piece. This may be done by passing the electric current through the test piece. 'I'his causes a magnetic condition most favorable for the detection of cracks which run longitudinally of the test piece and parallel of its major axis. Also, the current testing does not produce polar effects at the end of the test piece and inspectionmay be carried close to the ends.

The current for the electromagnet 5 is supplied which may be either a direct current generator or alternating current generator, When an object of soft iron or steelis to be tested, the current is allowed to remain on during testing. When a hard steel object is to be tested, the current can be applied and the object permanently magnetized. When alternating current is used for magnetizing a hardened steel article, the switch 2i should be such as to break the current at the end of a half current cycle. When this is done the object is left permanently magnetized. The magnetism imparted by the previous half cycle is left in the article. For this purpose the preferred form of switch is a mercury switch, as shown .in Figure 2, which consists of a' tube 22 having two contacts 28 and 24 extending through it and into a pool of mercury 25. When the tube is tilted to the right aboout its axis 26 the mercury flows to the other end of the tube and the circuit is broken. It is one of the characteristics of such a mercury switch that the current-is broken at the end of a half cycle when the current reaches" zero value. While I prefer to use the mercury from;-a,suitable source, such as a generator 28,

break switch in order to insure the breaking of the current at substantially the end of a half current cycle, other forms of switches may be used. For example, a switch having contacts made of some relatively fusible metal, such as brass or copper, and which has a not too fast separation of the contacts, will break the current at substantially the end of a half current cycle. The readily fusible metal forms a metallic arc and if the contacts are separated relatively slowly, such are persists until the end of the half current cycle.

In case it is desired to demagnetize the article after the testing, as, for example, a hardened steel article, the article can be demagnetized by means of the electromagnet 5 by passing an alternating electric current through it and gradually reducing the value of the current to substantially zero by means of a variable resistance 21.

The electric contacts I and I may be supplied with either direct or alternating current. For this purpose the leads II and II to the contact pieces I and i are connected with a double pole double throw switch 32. when the switch 32 is thrown to the left as shown in Figure 1, the

current from the battery I! is passed through the test piece 2. The passage of the current through the test piece induces magnetism therein, the magnetic lines of force running circumferentially around the test piece.

when the switch 32 is thrown to the right, the test piece is connected to alternating current. For this purpose there is provided a step-down transformer ll whose primary is connected with an alternating current generator 35. A switch It is provided preferably of the same character as the switch 2!, whereby alternatingcurrent may be used, if desired, for permanently magnetizing a hardened steel article.

The article may be demagnetized by passing the alternating current through it and gradually reducing the current to substantially zero by means of a variable resistance 81. I 1

As will appear from the above description, the test piece may be subjected in one testing appara-- tus to both longitudinally and transversely di-- rected lines of magnetic flux. Not only the direction, but also the distribution of the magnetic flux can be controlled by the apparatus. A magnetic flux which is distributed substantially uniformly through the body of the test piece can be secured by magnetizing it by means of the electromagnet 5, particularly when direct current is used for this purpose. On the other hand, a concentration of the magnetic flux at the surface of the article can be secured by magnetizing it by passing an alternating current through the article. In this case the magnetic flux is concentrated at the surface due to the skin effect produced by the current alternations. This distribution of flux is particularly desirable for detecting surface flaws.

After the test piece has been tested by applying the finely divided magnetic material as described in my Patent 1,960,898, it can be demagnetized in the same apparatus as above ex- Dlained.

In Figure 4 is illustrated a modification intended for the testing of shorter more chunky pieces of material. This form of apparatus comprises a base having an upright ll carrying an electromagneticcdlll. Anarmflisadiustableon the upright ll by meansof a gear ll meshing with rackteethllintheumllhti Thebasellhasa magnetic pole piece 48 and the arm 43 carries a complementary pole piece 1. Conducting plates III and ii are provided for the pole pieces 48 and 41 respectively, and are insulated therefrom by insulation 52.

The piece to be tested is clamped between the pole pieces 46 and 41 which carry the contacts 50 and BI when testing is to be carried out by passing the electric current through the test piece. When the testing is to be carried out by the applied magnetism from the electromagnet 42, the contact pieces 50 and iii are removed so as to bring the iron pole pieces into direct contact with the article.

The object to be tested may be clamped in different positions between the pole pieces 46 and 41, to thereby produce magnetic fluxes in different directions in the object to be tested. In this way effective testing for cracks running in different directions may be had. The differences in direction of the magnetic fluxes may also be secured by testing with the electromagnet which produces flux in a vertical direction, and by passing the electric current through the object which produces a circumferential flux in the horizontal direction.

The current connections for the electromagnet l2 and the contacts 5! and SI are similar to those shown in Figure l and corresponding reference characters are used therefor.

While I have illustrated and described the preferred embodiment of my invention, it is to be understood that the invention may be otherwise embodied and practiced within the scope of the following claims.

I claim:

1. Apparatus for the magnetic testing of objects of paramagnetic material. comprising an electromagnet having adjustable pole pieces for engaging the object, and contact pieces carried by the pole pieces for also engaging the object to pass an electric current directly through the object.

Apparatus for the magnetic testing of obfleets of paramagnetic material, comprising an electromagnet having adjustable pole pieces for engaging the object to be tested, electrical contacts carried by the pole pieces, and means. for moving the contacts against the object to be tested and raising it away from the pole pieces, and means for supplying electric current to the contact pieces.

3. Apparatus for the magnetic testing of obiects of paramagnetic material, comprising an electromagnet having adjustable pole pieces for engaging the object to be tested, contact plates arranged to be interposed between the pole pieces and the piece to be tested, and means for supplying current to the contact plates.

4. Apparatus for the magnetic testing of objects of paramagnetic material, comprising an electromagnet having pole pieces for engagingthe object, means for supplying electric current to the electromagnet, electric contacts on said pole. pieces for engaging the object, and means for supplying electric current to said contacts.

5. Apparatus for the magnetic testing of ob-' jects of paramagnetic material, comprising means including contact pieces for producing magnetic flux in one direction in the object and means on said contact pieces for producing a magnetic flux in the object at an angle to the first flux.

6. Apparatus for the magnetic testing of ob- Jects of paramagnetic material, comprising an electromagnet having pole pieces engaging the object, electric contact pieces mounted-on said pole pieces adapted to be brought into contact with the object to be tested for passing electric current directly through said object to magnetize said object, and means for passing an alternating current of decreasing intensity through said cb-Y ject to demagnetize the same.

'1. Apparatus for the magnetic testing of objects of paramagnetic material, comprising an electromagnet for magnetizing the object, means i for supplying a magnetizing current to the elec- 10 tromagnet, electric contacts mounted on the pole of said electromagnet for engaging the object, means for supplying an alternating current to said contacts, and means for gradually reducing 'the alternating current to .demagnetize the ob- 15 ject.

8. Apparatus for the magnetic testing of objects of paramagnetic material, comprising an eiectromagnet for magnetizing the object, means rent. through the electromagnet, electrical con 'tacts movably mounted on the poles of said elecv for passing either a direct or an=alternating curtromagnet for engaging the object, and means electromagnet for producing a flux through the object in one direction, and means on the poles of said electromagnet for passing current directly through the object to produce a magnetic flux in another direction in the object.

i V. BE FOREST. 

